Here's another thought. I haven't read the Opie book (not everyone has access to a good library, Malcolm, nor time to visit one during operating hours!) It seems to me, though (please correct me if I'm wrong, as it's late and I'm sleepy) that the argument put forth above goes something like this:
(1) "Ring Around a Rosy" can be found in an early form, which does not include elements like ashes and falling down.
(2) Those elements (ashes, etc.) are the ones that suggest to some people a reference to plague (let's leave the precise century open for now)
(3)Therefore, "Ring Around a Rosy" has nothing to do with plague.

It seems to me, though, that this argument is flawed. Isn't it possible that there is another song/poem which did refer to the Great Plague (or another one), and which then later became conflated with "Ring Around a Rosy"? If this were the case, then there would be some validity to the position that the rhyme as it exists today does in fact refer to plague.

Does this makes any sense to the scholars? Or to anyone? Or should I just go back to the beach?

Aloha,
Mark